c
c a small tree
c green vertices must have a blue successor, so leaves cannot be green
c blue nodes cannot have any blue children
c at least one node in 2, 3, 4 must be green, and thus have a blue successor
c at least one node must not be red
c
p edge 7 6
e 1 2
e 1 3
e 1 4
e 2 5
e 3 6
e 4 7

